Quest bug: "The Many Asses of Dr. Mephesto"

[dr. f. otze]

Slight spoilers ahead. In the mission "the many asses of Dr. Mephesto" you meet the freedom pals outside of Dr. Mephesto's gate. A cutscene launches in which Dr. Mephesto tells the boys to wait until nighttime. After some looking around i checked a walkthrough on how to continue (https://www.youtube.com/watch?v=A6xofU2Qnw8). Morgan Freeman is supposed to appear to teach you a new fart-power and activate the vent next to the gate. I've left the game running for several hours and nothing has happened. I can't continue the game until Morgan Freeman appears.

Has anyone else here had a similar bug? Thanks in advance for any support.